There are many medical procedures where imaging of blood vessels and other body lumens or internal cavities is desirable in order to ascertain the extent of plaque, stenosis, obstructions or other pathologies that may exist. A prior art technique of providing an image of a lumen employs X-ray fluoroscopy. In X-ray fluoroscopy, a contrast agent is sent through an artery of interest. The contrast agent is visible under X-ray radiation which enables an X-ray system to provide an image of the arterial obstruction. However, such X-ray imaging techniques have disadvantages. An X-ray image of an arterial obstruction is a profile of the contrast agent as it flows through the artery. Therefore, the images provided are generally of the contrast agent in a single plane of view, not of the tissue. Moreover, the true lumen diameter is generally not provided by these images. In addition, the characteristics of the plaque within the artery are not provided, which is important in determining the success of a possible angioplasty procedure. Another disadvantage is the potential harmful effects of the radiation to the patient and attending medical personnel. Furthermore, there is potential for additional harmful effects due to the contrast agent.
Other prior art imaging techniques utilize catheter technology to obtain an image of an area within a body lumen. One such system utilizes a catheter and a transducer, as shown in FIG. 1, in conjunction with an ultrasound imaging system to provide an image of an area. Ultrasonic imaging techniques are well suited for the imaging of the soft tissue found in body lumens. Moreover, ultrasonic energy is useful in the location of a catheter that has been directed into a body. In this regard, reference is made to U.S. Pat. No. 5,076,278 entitled ANNULAR ULTRASONIC TRANSDUCERS EMPLOYING CURVED SURFACES USEFUL IN CATHETER LOCALIZATION which issued on Dec. 31, 1991 to Vilkomerson et al. In addition, ultrasonic energy is not detrimental to the health or safety of attending physicians or other medical personnel.
In prior art ultrasound imaging systems, a transducer is utilized that emits an ultrasonic imaging beam. The transducer is fastened about the outside circumference of a catheter and the ultrasonic imaging beam emanates perpendicular to the catheter. Because of this, the transducer only provides an image of areas on the sides of the catheter, as shown in FIG. 1. Such prior art catheter side scanning systems generally do not provide an image of the central region of the lumen in front of the catheter tip. This is a disadvantage since it is the central region of the lumen that should be imaged in order to characterize a severe stenosis.
In addition, such prior art side scanning systems proceed blindly forward through the blood vessel as the catheter is moved. This forward, unchecked motion may inadvertently cause the catheter to contact the blood vessel wall and shear off material attached to the blood vessel wall so that it is pushed into the bloodstream. Furthermore, such prior art side scanning systems generally do not provide for the guidance of therapeutic procedures such as laser ablation or mechanical atherectomy. Moreover, prior art catheter side scanning systems provide a plane image on the side of the catheter, which prevents a substantial portion of many pathologies from being characterized.
It would be advantageous in such procedures to allow the physician or other medical personnel to view an area or volume in front of the catheter or probe tip as the catheter is moved through the lumen. In this way, the physician could view an oncoming area to anticipate an oncoming obstruction as the probe is moved to an area of interest. In addition, it would be advantageous to provide several image planes of a pathology being imaged in order to optimally characterize the pathology.
Another prior art technique utilizes a catheter that is volume imaging and front looking but does not employ ultrasonic imaging techniques. U.S. Pat. No. 4,998,916 to Hammerslag, et al discloses a steerable catheter device for coronary angioplasty applications. The device can negotiate the tortuous character of a vascular system. Fiber optic bundles are located at the tip of the device that illuminate an area in front of the device. In order to visualize a volume, a transparent inert liquid, such as a saline solution, must be discharged into the vascular system. The transparent liquid is discharged in front of the device and displaces blood from the front of the device. This enables a user to view through the liquid and observe the volume in front of the device.
However, systems employing fiber optics have disadvantages. One disadvantage is that essentially only the surfaces of the pathologies can be seen. In addition, the liquid utilized must be replaced frequently since it will dissipate and is absorbed into the vascular system. Therefore, the amount of time that this prior art device can be used is dependent upon the ability of the patient's vascular system to absorb the liquid. Moreover, this technique is not particularly reliable and is time consuming to use and therefore relatively expensive.
The present invention circumvents the drawbacks in the prior art by providing an ultrasonic scanning system that can image an area or volume in front of the probe as the probe is moved through the lumen.